1. Field of the Invention
The present invention relates to a thin-film magnetic head used for magnetic recording, especially to a tape head for reading data from a magnetic tape and/or writing data to a magnetic tape. The present invention further relates to a magnetic tape apparatus provided with the tape head. The present invention furthermore relates to a method for controlling a magnetic spacing that is a distance between the end of the head element in the thin-film magnetic head and the surface of the magnetic record layer of the magnetic recording medium.
2. Description of the Related Art
In recent years, magnetic recording and reproducing apparatuses have been remarkably improved in capacity of storage data, corresponding to the widespread use of multimedia and the Internet. And magnetic tape apparatuses for backing up or storing data or for recording and reproducing audio video information are no exception of this trend of larger capacity, and have been required to be improved in areal recording density corresponding to the larger capacity.
Thin-film magnetic heads are widely used, in the above-described magnetic recording and reproducing apparatuses, for writing data to a magnetic recording medium and reading data from the medium. The thin-film magnetic heads have also been strongly required to be improved in performance corresponding to the larger capacity. Especially, it has been significantly important to appropriately control a magnetic spacing in order to stably perform read and write operations under higher recording density and to maintain original lifetime of the thin-film magnetic head. Here, the magnetic spacing is defined as a distance between the end of the head element of the thin-film magnetic head and the surface of the magnetic record layer of the magnetic recording medium.
One of the most effective methods for controlling the magnetic spacing is to adjust the pressure working between the thin-film magnetic head and the magnetic recording medium. For example, in a magnetic disk apparatus, the thin-film magnetic head flies above the rotating magnetic disk, and thus receives a certain negative pressure (a pressure by which the head and the medium are attracted to each other) generated by laminar air flow passing through between the head and the magnetic disk. Then, the negative pressure is balanced with an adjusted pressure which is brought to the head by the suspension that supports the head, to maintain a predetermined magnetic spacing.
As a measure for positively controlling the magnetic spacing by adjusting the pressure working between the thin-film magnetic head and the magnetic recording medium, for example, US Patent Publication No. 2003/0174430A1 describes a technique in which the head end surface is protruded toward the magnetic disk by heat generated from a heater provided within the thin-film magnetic head for magnetic disk apparatuses. Further, Japanese Patent Publication No. 2001-6143A describes a thin-film magnetic head in which a rail pattern having two steps is formed on an air bearing surface (ABS) to improve the accuracy in flying height.
Also in the thin-film magnetic head for a magnetic tape apparatus (tape head), it is an extremely effective method for appropriately controlling the magnetic spacing to adjust the pressure working between the tape head and magnetic tape. Here, the tape head and the magnetic tape as a magnetic recording medium are usually contacted with each other by receiving a certain suppress force that causes them to attract each other. Therefore, it is important for controlling the magnetic spacing to adjust the suppress force. As an example of intending to adjust the suppress force, Japanese Patent Publication No. 2004-295951A discloses a technique of utilizing a negative-pressure slider. Further, in the tape heads, it is significantly important to ensure a stable contact between the tape head and a running magnetic tape as a magnetic recording medium. As an approach for the stable contact, for example, U.S. Pat. No. 6,122,147 (Japanese Patent Publication No. 2000-207800A) discloses a technique in which cavities are provided in the medium-opposed surface of the tape head, and the cavities deform a portion of the magnetic tape passing by the cavities, to stably contact the tape head with the magnetic tape.
However, there has been a problem that the magnetic spacing is likely to vary due to the change in pressure working between the thin-film magnetic head and the magnetic recording medium. The change in pressure can be derived from the change in shape of the medium-opposed surface of the head, which is generated by the contact between the head and the medium, or from the burning and depositing of wear debris generated by the contact.
Especially, the tape head slides on the magnetic tape during read and write operations. Therefore, the shape of the tape bearing surface (TBS), which is a medium-opposed surface as well as a sliding surface, varies over time due to the friction with the magnetic tape. The variation of the shape becomes more drastic in the case that the magnetic tape contains abrasive. As the case may be, the lifetime of the tape head would be reduced by excessively decreasing the magnetic spacing due to the wear of the head generated from the increase in the degree of contact between the head and the magnetic tape. Further, in some cases, the head performance may be degraded due to frictional heat generated by the contact.
Furthermore, in some cases, the magnetic spacing may become larger due to the change in shape of the TBS or due to the burning and depositing of the wear debris described above, which would cause the read output to be decreased, or cause the peak steepness of the read signal to be degraded. Even in the tape head described in the above-described U.S. Pat. No. 6,122,147, constant is the negative pressure in the cavity by which the magnetic tape is attracted. Therefore, the tape head cannot control the magnetic spacing in response to the changing conditions.
Therefore, in the tape head, it is significantly important to appropriately control the magnetic spacing by dynamically and accordingly adjusting the pressure working between the head and the magnetic recording medium, according to the change of conditions such as the change over time. This adjustment of the pressure also becomes significantly important for other thin-film magnetic heads such as a thin-film magnetic head for magnetic disk.